In patients with Cystic Fibrosis, recurrent airway infection caused by Pseudomonas aeruginosa ultimately leads to chronic airway infection. The purpose of this study is to determine whether supplementary low-dose azithromycin to standard inhaled colistin and oral ciprofloxacin in the treatment of intermittent pseudomonas airway-infection can postpone the next episode of intermittent pseudomonas airway-infection and prevent development of chronic airway-infection.